We love it when people help us out.
Did a new version of Tika come out and you want to get the Nuget updated? This is very common so check out the Developer Guide on Updating Tika. After you've got the new version building, create a pull request. Once it is merged and a release is tagged a Nuget will be published.
Check out the Developer Guide. It should have everything you need technically to get started contributing.
This project typically has a few up for grabs issues.